On 06/19/2017 07:03 AM, Michal Kubecek wrote:
> Our customer encountered stuck NFS writes for blocks starting at specific
> offsets w.r.t. page boundary caused by networking stack sending packets via
> UFO enabled device with wrong checksum. The problem can be reproduced by
> composing a long UDP datagram from multiple parts using MSG_MORE flag:
>
> sendto(sd, buff, 1000, MSG_MORE, ...);
> sendto(sd, buff, 1000, MSG_MORE, ...);
> sendto(sd, buff, 3000, 0, ...);
>
> Assume this packet is to be routed via a device with MTU 1500 and
> NETIF_F_UFO enabled. When second sendto() gets into __ip_append_data(),
> this condition is tested (among others) to decide whether to call
> ip_ufo_append_data():
>
> ((length + fragheaderlen) > mtu) || (skb && skb_is_gso(skb))
>
> At the moment, we already have skb with 1028 bytes of data which is not
> marked for GSO so that the test is false (fragheaderlen is usually 20).
> Thus we append second 1000 bytes to this skb without invoking UFO. Third
> sendto(), however, has sufficient length to trigger the UFO path so that we
> end up with non-UFO skb followed by a UFO one. Later on, udp_send_skb()
> uses udp_csum() to calculate the checksum but that assumes all fragments
> have correct checksum in skb->csum which is not true for UFO fragments.
>
> When checking against MTU, we need to add skb->len to length of new segment
> if we already have a partially filled skb and fragheaderlen only if there
> isn't one.
>
> In the IPv6 case, skb can only be null if this is the first segment so that
> we have to use headersize (length of the first IPv6 header) rather than
> fragheaderlen (length of IPv6 header of further fragments) for skb == NULL.
>
> Fixes: e89e9cf539a2 ("[IPv4/IPv6]: UFO Scatter-gather approach")
> Fixes: e4c5e13aa45c ("ipv6: Should use consistent conditional judgement for
> ip6 fragment between __ip6_append_data and ip6_finish_output")
> Signed-off-by: Michal Kubecek <mkube...@suse.cz>
LGTM.
Acked-by: Vlad Yasevich <vyase...@redhat.com>
-vlad
> ---
> net/ipv4/ip_output.c | 3 ++-
> net/ipv6/ip6_output.c | 2 +-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 7a3fd25e8913..532b36e9ce2a 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -964,7 +964,8 @@ static int __ip_append_data(struct sock *sk,
> csummode = CHECKSUM_PARTIAL;
>
> cork->length += length;
> - if ((((length + fragheaderlen) > mtu) || (skb && skb_is_gso(skb))) &&
> + if ((((length + (skb ? skb->len : fragheaderlen)) > mtu) ||
> + (skb && skb_is_gso(skb))) &&
> (sk->sk_protocol == IPPROTO_UDP) &&
> (rt->dst.dev->features & NETIF_F_UFO) && !dst_xfrm(&rt->dst) &&
> (sk->sk_type == SOCK_DGRAM) && !sk->sk_no_check_tx) {
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index bf8a58a1c32d..1699acb2fa2c 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1390,7 +1390,7 @@ static int __ip6_append_data(struct sock *sk,
> */
>
> cork->length += length;
> - if ((((length + fragheaderlen) > mtu) ||
> + if ((((length + (skb ? skb->len : headersize)) > mtu) ||
> (skb && skb_is_gso(skb))) &&
> (sk->sk_protocol == IPPROTO_UDP) &&
> (rt->dst.dev->features & NETIF_F_UFO) && !dst_xfrm(&rt->dst) &&
>
